Try to add Array Texture (GL_TEXTURE_2D_ARRAY) support for OpenGL 3 backend but cannot complete it

[eminor1988]

Version: 1.87
Branch: docking

Backend: imgui_impl_opengl3.cpp

Array Texture:
https://www.khronos.org/opengl/wiki/Array_Texture

I added a macro - "#define IMGUI_IMPL_OPENGL_USE_TEXTURE_2D_ARRAY 1" to switch texture to Array Texture (GL_TEXTURE_2D_ARRAY).

It works fine but the current OpenGL 3 backend code contains GLSL version 120 (OpenGL 2.1) code should not presented in OpenGL 3 core profile, it cannot promise to support Array Texture feature, so I don't know how to deal it.

The GLSL 120 code might be related with the issue - #1513

Other related issue - #3198

Does anyone can help ?

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My changes:
changes.patch.txt

[ocornut]

Your backend is actually misnamed and should work with 2.x (as per #1900, in particular #1900 (comment))

Up to you how to want to support this. I suppose users of IMGUI_IMPL_OPENGL_USE_TEXTURE_2D_ARRAY won't use 2.X anyway. Either way I don't think we would merge a PR like that into the official backend, seems unnecessary. As highlighted in #3198 if you want to render your own stuff from texture array use ImDrawList callback to temporarily change the state of the renderer.

[eminor1988]

Got it, I will try to workaround it by the callback solution.

Other possible solution to me:

1. Just Copy/Blit single layer of GL_TEXTURE_2D_ARRAY array texture into a GL_TEXTURE_2D texture, but it need additional cost (GPU/VRAM) to copy the texture and determine when to release the copied texture (become non-immediate-mode style).
2. Use glTextureView but it requires OpenGL 4.3, so it cannot be used it in WebGL 2.

Thanks.